Water-insoluble, water-swellable, hydrogel-forming absorbent polymers are capable of absorbing large quantities of liquids such as water, blood, body exudates (e.g., urine, menstrual fluid), industrial fluids and household fluids and are further capable of retaining such absorbed liquids under moderate pressures. The absorption characteristics of such polymer materials make them especially usefull for incorporation into absorbent articles such as diapers, sanitary napkins, tampons, and the like.
In general, conventional absorbent polymer materials have good or required absorption characteristics to water and urine; however, there still remains poor distribution and dispersion with certain liquids. In particular, they have poor absorption characteristics for certain liquids, specifically for blood or menstrual fluid. More specifically, upon contacting blood or menstrual fluid, absorbent polymer materials do not show enough absorption characteristics, especially the rate of blood absorption due to their poor distribution and dispersion of blood.
Such poor distribution and dispersion of blood is mainly caused by poor wettability with blood. In general, ability of the distribution and dispersion of blood can be evaluated by measuring the contact angle of blood on the surface of absorbent polymer material. Since contact angles of conventional absorbent polymer materials are in the range of from about 30 degree to about 90 degree or more, desired wettability with blood cannot be obtained whereby the poor distribution and dispersion of blood are caused in the absorbent polymer materials.
One attempt to improve such absorption characteristics is disclosed in U.S. Pat. No. 4,190,563 (Rosley et al.), issued Feb. 20, 1980, wherein the wettability with blood is improved by surface treatment of particulate absorbent polymer materials using polyethers. The disclosed absorbent polymer materials can be effectively wetted with blood; however, the distribution and dispersion of the blood into and among the absorbent polymer materials is not fully improved because of their high resistance to liquid flow within the polymer materials due to lack of capillary or liquid transport channels, and insufficient specific surface area of the polymer materials. Therefore, the absorption characteristics with blood is not satisfactory and there remains a need to improve further the distribution and dispersion of blood through and among absorbent polymer materials.
In addition, since the polyether are just coated or physically bonded on the surface of absorbent polymer materials, such polyether can be washed away from the absorbent polymer materials by succeeding application of liquids.
Consequently, there remains a need for further improvements in such absorbent materials.
Therefore, one object of the present invention is to provide a porous absorbent material which has improved absorption characteristics with liquids.
Another object of the present invention is to improve distribution and dispersion of liquids in an absorbent material.
Yet another object of the present invention is to improve the rate of absorption of an absorbent material, especially for blood.
Still another object of the present invention is to provide an absorbent material which is not affected by succeeding application of liquids.
Yet another object of the present invention is to provide a method for making such absorbent materials.
Still another object of the present invention is to provide absorbent disposable articles, such as diapers, sanitary napkins, tampons, and the like, which have improved absorption characteristics with body exudates.